Permanent magnet rotating electric machine

ABSTRACT

A permanent magnet rotating electric machine uses no skewing under a predetermined current and voltage condition to prevent torque from decreasing and to decrease pulsation torque to make the machine less vibrating and less noisy. The permanent magnet rotating electric machine includes a stator with multi-phase stator windings and a rotor with a plurality of permanent magnets internally embedded in a rotor core. The core shape of the rotor is uniform in the depth (longitudinal) direction with no skewing in the arrangement of the permanent magnets. The permanent magnets are symmetrical with respect to the rotation direction, but irregular with respect to the depth direction, for each pole. A magnetic flux generated from the between-pole permanent magnets almost equals a magnetic flux generated from the pole-center permanent magnet.

BACKGROUND OF THE INVENTION

The present invention relates to a permanent magnet rotating electricmachine that has a rotor built with a plurality of permanent magnetsembedded in a rotor core.

A conventional permanent magnet rotating electric machine is disclosed,for example, in JP-A-9-327140. In such a permanent magnet rotatingelectric machine, the rotor core is fixed on the shaft and the rotor isbuilt by inserting a plurality of permanent magnets, each with arectangular cross section, from the shaft direction into the storagesection formed on the rotor core so that the rotor can rotate with apredetermined gap to the inner periphery of the stator core within thestator. The permanent magnets are magnetized such that the north poleand the south pole alternate.

A motor with rectangular magnets embedded in the rotor, such as the onedescribed above, is efficient during high-speed rotation because fieldweakening is effective during high-speed rotation. For this reason, themotor is used, for example, as the permanent magnet motor on an electriccar where high-speed rotation is required. To avoid vibrations andnoises generated during driving, the magnets within the rotor are splitin the longitudinal direction to produce semi-slot skews for attaininglow-torque pulsation.

The motor torque of a magnet-embedded rotating electric machine such asthe one described above is expressed by expression (1) given below.T=φIq+(Lq−Ld)Iq×Id   (1)where, T is the motor torque, φ is the magnetic flux of the permanentmagnet, Lq is the q-axis inductance, Ld is the d-axis inductance, Iq isthe q-axis winding current, and Id is the d-axis winding current.

In expression (1), the first term is the torque of the major magneticflux of the permanent magnet, and the second term is a reluctance torquegenerated by the auxiliary magnetic pole of an iron core between twomagnets. The magnetic torque has a period for each pole pair (electricalangle of 360 degrees), while the reluctance torque has a period for eachpole (electrical angle of 180 degrees).

In this case, if the rotor is skewed as in the prior art example, themaximum torque is decreased because of a difference in the current phasefor generating the maximum torque. If the magnet torque is the maintorque, the torque decrease is small, for example, about 5% because themagnetic torque has a period of 360 degrees; however, if the reluctancetorque is the main torque, the torque decrease is large, for example,about 10% because the reluctance torque has a period of 180 degrees.Thus, for a motor that uses the reluctance torque as the main toque,there has been a need for a shape that reduces torque pulsation with noskewing.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a permanent magnetrotating electric machine that uses no skewing under a predeterminedcurrent and voltage condition to prevent torque from decreasing and, atthe same time, decreases pulsation torque to make the machine lessvibrating and less noisy.

(1) To achieve the above object, a permanent magnet rotating electricmachine according to the present invention comprises a stator on whichmulti-phase stator windings are provided and a rotor which is built byembedding a plurality of permanent magnets internally into a rotor coreand which is rotatably arranged with a predetermined gap to the stator,a core shape of the rotor being uniform in a depth (longitudinal)direction, wherein a plurality of permanent magnets are arranged foreach pole of the rotor and wherein the plurality of permanent magnetsare symmetrical with respect to a rotation direction but irregular withrespect to the depth direction.

This configuration allows a permanent magnet rotating electric machine,with no skewing under a predetermined current and voltage condition, toprevent torque from decreasing and to decrease pulsation torque, thusmaking the machine less vibrating and less noisy.

(2) Preferably, in (1) described above, there are, for each pole, threeor more permanent-magnet-inserting holes through which the permanentmagnets are inserted into the rotor.

(3) Preferably, in (1) described above, the ratio of the length of onepermanent magnet arrangement to the length of another permanent magnetarrangement in the depth direction of the rotor is 1:1.

(4) Preferably, in (1) described above, θ satisfies a relationθ=(n+0.5)×τs+φ (n is an integer) wherein, for each pole of the rotor, θis an angle between between-pole permanent-magnet-inserting holes withits vertex at a center of a shaft, φ is an angle of a pole-centerpermanent-magnet-inserting hole with its vertex at the center of theshaft, and τs is a slot pitch.

(5) Preferably, in (1) or (4) described above, a magnetic flux generatedfrom between-pole magnets equals a magnetic flux generated from apole-center permanent magnet for each pole of the rotor.

Other objects, features and advantages of the invention will becomeapparent from the following description of the embodiments of theinvention taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partial cross section, viewed from the front, of a permanentmagnet rotating electric machine in a first embodiment of the presentinvention.

FIG. 2 is a skeleton perspective view in the rotor depth (longitudinal)direction of a rotor, illustrating the magnet arrangement structure inthe permanent magnet rotating electric machine in the first embodimentof the present invention.

FIG. 3 is a side view showing the structure of the stator and the rotorof the permanent magnet rotating electric machine in the firstembodiment of the present invention.

FIG. 4 is a diagram showing the result of magnetic field analysis thatis made by inserting magnets into the between-pole inserting holes ofthe permanent magnet rotating electric machine in the first embodimentof the present invention.

FIG. 5 is a diagram showing the result of magnetic field analysis thatis made by inserting a magnet into the pole-center inserting hole of thepermanent magnet rotating electric machine in the first embodiment ofthe present invention.

FIG. 6 is a diagram showing a torque pulsation when magnets are insertedinto the between-pole inserting holes of the permanent magnet rotatingelectric machine in the first embodiment of the present invention.

FIG. 7 is a diagram showing a torque pulsation when a magnet is insertedinto the pole-center inserting hole of the permanent magnet rotatingelectric machine in the first embodiment of the present invention.

FIG. 8 is a diagram showing a torque pulsation in the permanent magnetrotating electric machine in the first embodiment of the presentinvention.

FIG. 9 is a diagram showing the structure of the stator and the rotor ofa permanent magnet rotating electric machine in a second embodiment ofthe present invention and showing the result of magnetic field analysisthat is made by inserting magnets into the between-pole inserting holes.

FIG. 10 is a diagram showing the result of magnetic field analysis thatis made by inserting a magnet into the pole-center inserting hole of thepermanent magnet rotating electric machine in the second embodiment ofthe present invention.

FIG. 11 is a skeleton perspective view in the rotor depth (longitudinal)direction of a rotor, illustrating the magnet arrangement structure in apermanent magnet rotating electric machine in a third embodiment of thepresent invention.

FIG. 12 is a diagram showing the structure of the stator and the rotorof a permanent magnet rotating electric machine in a fourth embodimentof the present invention and showing the result of magnetic fieldanalysis that is made by inserting magnets into the between-poleinserting holes.

FIG. 13 is a diagram showing the result of magnetic field analysis thatis made by inserting a magnet into the pole-center inserting hole of thepermanent magnet rotating electric machine in the fourth embodiment ofthe present invention.

FIG. 14 is a diagram showing the structure of the stator and the rotorof a permanent magnet rotating electric machine in a fifth embodiment ofthe present invention and showing the result of magnetic field analysisthat is made by inserting magnets into the between-pole inserting holes.

FIG. 15 is a diagram showing the result of magnetic field analysis thatis made by inserting a magnet into the pole-center inserting hole of thepermanent magnet rotating electric machine in the fifth embodiment ofthe present invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The configuration of a permanent magnet rotating electric machine in afirst embodiment of the present invention will be described below withreference to FIGS. 1-8. In the example below, the present invention isapplied to a three-phase, 8-pole/48-slot permanent magnet rotatingelectric machine.

First, referring to FIG. 1, the general configuration of the permanentmagnet rotating electric machine in the first embodiment of the presentinvention will be described.

FIG. 1 is a partial cross section, viewed from the front, of thepermanent magnet rotating electric machine in the first embodiment ofthe present invention.

Referring to FIG. 1, a stator 20 of a rotating electric machine 10comprises a stator core 22, a multi-phase stator winding 24 wound on thestator core 22, and a housing 26 that holds the stator core 22 on theinner periphery side. A rotor 30 comprises a rotor core 32, a permanentmagnet 36 inserted into a permanent-magnet-inserting hole 34 provided onthe rotor core 32, and a shaft 38. The shaft 38 is held rotatably bybearings 42 and 44. The bearings 42 and 44 are held by end brackets 46and 48 fixed on the sides of the housing 26.

A magnetic pole position detector PS that detects the position of thepermanent magnet 36 of the rotor 30 and an encoder E that detects theposition of the rotor 30 are provided to the side of the rotor 30. Therotating electric machine 10 is operated and controlled by a controller,not shown, using signals from the magnetic pole position detector PS andoutput signals from the encoder E.

Next, referring to FIG. 2, the arrangement structure of the magnets inthe permanent magnet rotating electric machine in the first embodimentof the present invention will be described.

FIG. 2 is a skeleton perspective view in the rotor depth (longitudinal)direction of the rotor, illustrating the magnet arrangement structure inthe permanent magnet rotating electric machine in the first embodimentof the present invention. The same reference numerals as those in FIG. 1indicate the same structural elements.

A plurality of permanent-magnet-inserting holes 34 are formed in therotor core 32 of the rotor 30. For a three-phase, 8-pole/48-slotpermanent magnet rotating electric machine, eightpermanent-magnet-inserting holes 34 are usually provided. However, thepermanent-magnet-inserting hole 34 of one pole in this embodimentcomprises three permanent-magnet-inserting holes, 34A, 34B, and 34C, asshown in the figure. Although the three permanent-magnet-inserting holes34A, 34B, and 34C, are shown for only one pole in the figure forconvenience of illustration, the permanent-magnet-inserting hole 34 ofeach of the other poles also comprises three permanent-magnet-insertingholes. The permanent-magnet-inserting holes 34A, 34B, and 34C, areparallel to the shaft of the rotor 30. That is, thepermanent-magnet-inserting hole 34 is not inclined, that is, not skewed,with respect to the shaft of the rotor. That thepermanent-magnet-inserting hole 34 is not skewed means that the rotorcore is of uniform shape in the depth direction (longitudinal).

Permanent magnets 36A, 36B, and 36C, which are rectangular solids, areinserted into the permanent-magnet-inserting holes 34A, 34B, and 34C,respectively. Therefore, one pole comprises a plurality of permanentmagnets 36A, 36B, and 36C. The longitudinal directions of the permanentmagnets 36A, 36B, and 36C, each parallel to the shaft of the rotor, arenot skewed.

If the length of the permanent-magnet-inserting holes 34A, 34B, and 34Cis L (L equals the length of the rotor 30 in the shaft direction), thenthe length of the permanent magnets 36A, 36B, and 36C is L/2,respectively. When the permanent magnets 36A and 36C are arranged on theleft side in the shaft direction of the rotor 30, the permanent magnet36B is arranged on the right side in the shaft direction of the rotor30. Because the permanent magnets 36A and 36C are arranged on both sidesof the permanent magnet 36B in the rotational direction of the rotor,the plurality of permanent magnets 36A, 36B, and 36C are arrangedsymmetrically with respect to the pole. However, because the permanentmagnets are arranged asymmetrically with respect to the depth direction(shaft direction) of the rotor 30, they are arranged irregularly withrespect to the longitudinal direction (depth direction, shaft direction)of the rotor 30.

The rotor 30 is arranged such that it is opposed to the inner peripheryof the stator 20 as shown in FIG. 1. When the surface areas of thepermanent magnets 36A, 36B, and 36C opposed to the stator 20 are SA, SB,and SC, respectively, SA=SC and SA+SC=SB. As a result, the magnetic fluxgenerated by the permanent magnet 36B in the center of one pole of therotor equals the magnetic flux generated by the between-pole permanentmagnets 36A and 36C of one pole of the rotor.

Next, with reference to FIG. 3, the structure of the stator and therotor of the permanent magnet rotating electric machine in the firstembodiment of the present invention will be described.

FIG. 3 is a side view showing the structure of the stator and the rotorof the permanent magnet rotating electric machine in the firstembodiment of the present invention. This figure shows two poles, thatis, one pole pair, of a three-phase, 8-pole/48-slot permanent magnetrotating electric machine. In the figure, the reference numerals, whichare the same as those in FIG. 1, denote the same structural elements.

The stator 20 has the stator core 22 that is almost circular, and 48slots 26 are formed on the stator core 22. This figure shows 12 slots 26corresponding to one pole pair. In the slots 26, U-phase stator windings24 (U1), V-phase stator windings 24 (V1), and W-phase stator windings 24(W1) are inserted. An opening 27 is provided for each slot 26 on theinner periphery of the stator core 22.

On the other hand, the rotor 30 is built by fixing the rotor core 32 onthe shaft 38 with the permanent magnets 36A, 36B, and 36C inserted intothe permanent-magnet-inserting holes formed on the rotor core 32.

The rotor 30 is arranged rotatably within the stator with apredetermined gap 28 between the rotor and the inner periphery of thestator core 22. The rotor core 32 is structured by layering many siliconsteel plates each with permanent-magnet-inserting holes. As shown in thefigure, the permanent magnets 36 are magnetized such that the polarityalternates between the N pole and the S pole for each pole.

For each pole of the rotor 30, let θ be the angle between between-polepermanent-magnet-inserting holes 34A and 34C with its vertex at thecenter of the shaft (in the figure, the angle between the left corner ofthe part on the stator opposed to the inserting hole 34C (where magneticflux is generated) and the right corner of the part on the statoropposed to the inserting hole 34A (where magnetic flux is generated)),let φ be the angle of the pole-center permanent-magnet-inserting hole34B with its vertex at the center of the shaft (in the figure, the anglebetween the left corner of the part on the stator opposed to theinserting hole 34B and the right corner of the part on the statoropposed to the inserting hole 34B), and let τs be the slot pitch(spacing between adjacent slots 26). Then, inserting Neodymium permanentmagnets 36A, 36B, and 36C based on the relation indicated by expression(2) gives an efficient result:θ=(n+0.5)×τs+φ  (2)where, n is an integer.

For a three-phase, 8-pole/48-slot permanent magnet rotating electricmachine, the slot pitch τs is the mechanical angle of 7.5° (electricalangle of 30°). Therefore, if n=1 in expression (2), θ=22.5° (mechanicalangle) (electrical angle of 90°) when φ=11.25° (mechanical angle)(electrical angle of 45°). That is, the magnetic flux generated by thefirst term on the right side of expression (2) equals the magnetic fluxgenerated by the second term.

Next, with reference to FIGS. 4 and 5, the magnetic field analysisresult of the permanent magnet rotating electric machine in the firstembodiment of the present invention will be described.

FIG. 4 is a diagram showing the result of magnetic field analysis thatis made by inserting magnets into the between-pole inserting holes ofthe permanent magnet rotating electric machine in the first embodimentof the present invention. FIG. 5 is a diagram showing the result ofmagnetic field analysis that is made by inserting a magnet into thepole-center inserting hole of the permanent magnet rotating electricmachine in the first embodiment of the present invention. Those figuresshow one pole of a three-phase, 8-pole/48-slot permanent magnet rotatingelectric machine. In the figures, the reference numerals, which are thesame as those in FIG. 3, denote the same structural elements.

FIG. 4 shows the result of magnetic field analysis when magnets areinserted into the between-pole inserting holes. That is, the figureshows the result of magnetic field analysis that is made by insertingthe permanent magnets 36A and 36C into the between-pole magnet-insertingholes 34A and 34C, respectively, with no permanent magnet in thepole-center magnet-inserting hole 34B. The broken line indicates amagnetic field.

FIG. 5 shows the result of magnetic field analysis when a magnet isinserted into the pole-center inserting hole. That is, the figure showsthe result of magnetic field analysis that is made by inserting thepermanent magnet 36B into the pole-center magnet-inserting hole 34B withno permanent magnet in the between-pole magnet-inserting holes 34A and34C. The broken line indicates a magnetic field.

Next, with reference to FIGS. 6-8, the torque pulsation of the permanentmagnet rotating electric machine in the first embodiment of the presentinvention will be described.

FIG. 6 is a diagram showing a torque pulsation when magnets are insertedinto the between-pole inserting holes in the permanent magnet rotatingelectric machine in the first embodiment of the present invention. FIG.7 is a diagram showing a torque pulsation when a magnet is inserted intothe pole-center inserting hole of the permanent magnet rotating electricmachine in the first embodiment of the present invention. FIG. 8 is adiagram showing a torque pulsation in the permanent magnet rotatingelectric machine in the first embodiment of the present invention. Thefigures show the torque pulsation for one pole of a three-phase,8-pole/48-slot permanent magnet rotat1ing electric machine.

FIG. 6 shows the torque pulsation for one pole (electrical angle of180°) when the magnets are inserted into the between-pole insertingholes as shown in FIG. 4.

FIG. 7 shows the torque pulsation for one pole (electrical angle of180°) when the magnet is inserted into the pole-center inserting hole asshown in FIG. 5.

Because the cores in FIG. 4 and FIG. 5 are of the same shape, they havean equal reluctance torque. In addition, because the magnet surface areais sized such that the cores have an almost equal magnet flux(S1+S3=S2), they have an almost equal magnet torque. Therefore, theaverage torque in FIG. 6 equals the average torque in FIG. 7.

As seen in the waveform shown in FIG. 6, six periods of torque pulsationare generated for one pole (48 periods for rotation), one for each slot.A torque pulsation is generated by the difference in magnetic fluxconcentration between the iron teeth and the gap slot. The waveform of atorque pulsation is closely related to the magnet pole-arc angle and, asthe pole-arc angle changes, the waveform of the torque pulsationchanges. The waveform of the torque pulsation in FIG. 7 with thepole-arc angle of φ, where θ=(n+0.5)×τs+φ, is the reverse of thewaveform of the torque pulsation in FIG. 6 with the pole-arc angle of θ.

Therefore, when the magnets in FIG. 3 and FIG. 4 are arranged half andhalf in the longitudinal direction as in this embodiment, combining thetorque pulsation shown in FIG. 6 with the torque pulsation shown in FIG.7 produces the torque pulsation shown in FIG. 8. As apparently indicatedby the torque waveform shown in FIG. 8, the torque pulsation is reducedin this embodiment. Calculating the ripple rate for use in comparisonindicates that the ripple rate is 22% in FIGS. 6 and 7, and 4% in thisembodiment as shown in FIG. 8. This is an 18% improvement in the ripplerate. This reduction in the pulsation torque minimizes the vibration andthe noise of the permanent magnet rotating electric machine.

As described above, this embodiment reduces the torque pulsation byarranging the permanent magnets symmetrically with respect to therotation direction but irregularly with respect to the depth directionfor each pole of the rotor of the permanent magnet rotating electricmachine and, in particular, by making θsatisfy the relationθ=(n+0.5)×τs+φ (n is an integer) wherein θ is the angle betweenbetween-pole permanent-magnet-inserting holes with its vertex at thecenter of the shaft, φ is the angle of the pole-centerpermanent-magnet-inserting hole with its vertex at the center of theshaft, and τs is the slot pitch. This embodiment makes it possible toprovide an electric vehicle that can run efficiently with a lessvibrating, less noisy motor.

Next, with reference to FIG. 9 and FIG. 10, the configuration of apermanent magnet rotating electric machine in a second embodiment of thepresent invention will be described. The general configuration of thepermanent magnet rotating electric machine in this embodiment is thesame as that shown in FIG. 1 and FIG. 2.

FIG. 9 is a diagram showing the structure of the stator and the rotor,and the result of magnetic field analysis when magnets are inserted intothe between-pole inserting holes, of the permanent magnet rotatingelectric machine in the second embodiment of the present invention. FIG.10 is a diagram showing the result of magnetic field analysis when amagnet is inserted into the pole-center inserting hole of the permanentmagnet rotating electric machine in the second embodiment of the presentinvention. In the figures, one pole of a three-phase, 8-pole/48-slotpermanent magnet rotating electric machine is shown. The referencenumerals in the figures, which are the same as those in FIG. 3, denotethe same structural elements.

As shown in FIG. 9, permanent-magnet-inserting holes 34A′, 34B′, and34C′ are each in the shape of an arc. They each have a columnarstructure with an arc-shaped cross section. Therefore, the permanentmagnets 36A′ and 36C′ inserted into the permanent-magnet-inserting holes34A′ and 34C′ also have a columnar structure with an arc-shaped crosssection.

FIG. 9 shows the result of magnetic field analysis when the magnets areinserted into the between-pole inserting holes. The broken lineindicates a magnetic field.

FIG. 10 shows the result of magnetic field analysis when a magnet isinserted into the central inserting hole, that is, when the permanentmagnet 36B′ is inserted into the central magnet inserting hole 34B′ withno permanent magnets in the between-pole inserting holes 34A′ and 34C′.The broken line indicates a magnetic field.

The use of arc-shaped permanent magnets increases the effective magneticfield and the torque that is generated.

The torque pulsation of the permanent magnet rotating electric machinein this embodiment are as shown in FIGS. 6 and 7. The torque pulsationof the whole rotating electric machine may be also reduced as shown bythe waveform of the torque pulsation that is a combination of the torquepulsation shown in FIG. 6 and the torque pulsation shown in FIG. 7.

As described above, this embodiment reduces the torque pulsation byarranging the permanent magnets symmetrically with respect to therotation direction, but irregularly with respect to the depth direction,for each pole of the rotor of the permanent magnet rotating electricmachine. This embodiment also makes it possible to provide an electricvehicle that can run efficiently with a less vibrating, less noisymotor.

Next, with reference to FIG. 11, the configuration of a permanent magnetrotating electric machine in a third embodiment of the present inventionwill be described. The general configuration of the permanent magnetrotating electric machine in this embodiment is the same as that shownin FIG. 1.

FIG. 11 is a skeleton perspective view in the rotor depth (longitudinal)direction of the rotor, illustrating the magnet arrangement structure inthe permanent magnet rotating electric machine in the third embodimentof the present invention. The same reference numerals as those in FIG. 1indicate the same structural elements.

A plurality of permanent-magnet-inserting holes 34 are formed in therotor core 32 of the rotor 30. For a three-phase, 8-pole/48-slotpermanent magnet rotating electric machine, eightpermanent-magnet-inserting holes 34 are usually provided. As in FIG. 2,one pole comprises three permanent-magnet-inserting holes, 34A, 34B, and34C. The permanent-magnet-inserting holes 34A, 34B, and 34C, areparallel to the shaft of the rotor 30. That is, thepermanent-magnet-inserting hole 34 is not inclined, that is, not skewed,with respect to the shaft of the rotor.

Permanent magnets 36A1, 36A2, 36B, 36C1, and 36C2, which are rectangularsolids, are inserted into the permanent-magnet-inserting holes 34A, 34B,and 34C, respectively. Therefore, one pole comprises a plurality ofpermanent magnets 36A1, 36A2, 36B, 36C1, and 36C2. The longitudinaldirections of the permanent magnets 36A1, 36A2, 36B, 36C1, and 36C2,each parallel to the shaft of the rotor, are not skewed.

If the length of the permanent-magnet-inserting holes 34A, 34B, and 34Cis L (L equals the length of the rotor 30 in the shaft direction), thenthe length of the permanent magnets 36A1, 36A2, 36C1, and 36C2 is L/4,respectively, and the length of the permanent magnet 36B is L/2. Whenthe permanent magnets 36A1, 36A2, 36C1, and 36C2 are arranged on theright and left sides in the shaft direction of the rotor 30, thepermanent magnet 36B is arranged in the center of the shaft direction ofthe rotor 30. Because the permanent magnets 36A1, 36A2, 36C1, and 36C2are arranged on both sides of the permanent magnet 36B in the rotationaldirection of the rotor, the plurality of permanent magnets 36A1, 36A2,36B, 36C1, and 36C2 are arranged symmetrically with respect to the pole.However, they are arranged irregularly with respect to the depthdirection (shaft direction) of the rotor 30.

The rotor 30 is arranged such that it is opposed to the inner peripheryof the stator 20 as shown in FIG. 1. When the surface areas of thepermanent magnets 36A1, 36A2, 36B, 36C1, and 36C2 opposed to the stator20 are SA1, SA2, SB, SC1, and SC2, respectively, SA1=SA2=SC1=SC2 andSA1+SA2+SC1+SC2=SB. As a result, the magnetic flux generated by thepermanent magnet 36B in the center of one pole of the rotor equals themagnetic flux generated by the between-pole permanent magnets 36A1,36A2, 36C1, and 36C2 of one pole of the rotor.

As described above, the magnets need not be arranged in the longitudinaldirection by halving them at the center as shown in FIG. 2. The magnetsmay also be arranged such that one part of the between-pole magnets andother part of the between-pole magnets each occupy ¼ and the centralmagnet occupies ½ to make the longitudinal direction ratio 1:1 as shownin FIG. 11.

The torque pulsation of the permanent magnet rotating electric machinein this embodiment is as shown in FIGS. 6 and 7. The torque pulsation ofthe whole rotating electric machine may be also reduced as shown by thewaveform of the torque pulsation that is a combination of the torquepulsation shown in FIG. 6 and the torque pulsation shown in FIG. 7.

As described above, this embodiment reduces the torque pulsation byarranging the permanent magnets symmetrically with respect to therotation direction, but irregularly with respect to the depth direction,for each pole of the rotor of the permanent magnet rotating electricmachine. This embodiment also makes it possible to provide an electricvehicle that can run efficiently with a less vibrating, less noisymotor. Next, with reference to FIG. 12 and FIG. 13, the configuration ofa permanent magnet rotating electric machine in a fourth embodiment ofthe present invention will be described. The general configuration ofthe permanent magnet rotating electric machine in this embodiment is thesame as that shown in FIG. 1 and FIG. 2.

FIG. 12 is a diagram showing the structure of the stator and the rotorof the permanent magnet rotating electric machine in the fourthembodiment of the present invention and the result of magnetic fieldanalysis when magnets are inserted into the between-pole insertingholes. FIG. 13 is a diagram showing the result of magnetic fieldanalysis when a magnet is inserted into the pole-center inserting holeof the permanent magnet rotating electric machine in the fourthembodiment of the present invention. In the figures, one pole of athree-phase, 8-pole/48-slot permanent magnet rotating electric machineis shown. The reference numerals in the figures, which are the same asthose in FIG. 3, denote the same structural elements.

In the examples shown in FIGS. 4 and 5 and FIGS. 9 and 10, the pole-arcangle of φ is 90° or lower and the magnet torque cannot be increased inorder for the pole-arc angle θ of the between-pole magnet-insertingholes to satisfy the relation θ=(n+0.5)×τs+φ where θ is the pole-arcangle of the between-pole magnet inserting holes, φ is the pole-arcangle in the center of the pole, and τs is the slot pitch.

To solve this problem, permanent-magnetic inserting holes 34A″ and 34C″each have a rectangular cross section with the longer side in the radiusdirection of the rotor, as shown in FIG. 12. The longer side of apermanent-magnet inserting hole 34B″ is in the circumferential directionof the rotor. A plurality of permanent magnets 36A″, 36B″, and 36C″ areinserted into the permanent-magnet inserting holes 34A″, 34B″, and 34C″as shown in FIG. 2. They may also be inserted as shown in FIG. 11. Thisconfiguration changes the part of the permanent-magnet surface areaopposed to the stator as follows. That is, the surface area of thepermanent magnets 36A″ and 36C″ becomes smaller than the surface area ofthe permanent magnet 36B″. Therefore, to make the magnetic fluxgenerated by the permanent magnets 36A″ and 36C″ equal to that generatedby the permanent magnet 36B″, the permanent magnet 36B″ is arranged nearthe center of rotation in the radius direction of the rotor to increasethe distance from the stator. FIG. 12 shows the result of magnetic fieldanalysis when the magnets 36A″ and 36C″ are inserted into thebetween-pole inserting holes. The broken line indicates a magneticfield.

FIG. 13 shows the result of magnetic field analysis when the magnet isinserted into the central inserting hole, that is, when the permanentmagnet 36B″ is inserted into the central magnet inserting hole 34B″ withno permanent magnets in the between-pole inserting holes 34A″ and 34C″.The broken line indicates a magnetic field.

Arranging the longer sides of the between-pole magnets 36A″ and 36C″ inthe radius direction as described above makes it possible for therelation θ=(n+0.5)×τs+φ and the magnetic flux equality conditioncompatible with high magnetic torques.

The torque pulsation of the permanent magnet rotating electric machinein this embodiment are as shown in FIGS. 6 and 7. The torque pulsationof the whole rotating electric machine may be also reduced as shown bythe waveform of the torque pulsation that is a combination of the torquepulsation shown in FIG. 6 and the torque pulsation shown in FIG. 7.

As described above, this embodiment reduces the torque pulsation andgenerates high torques by arranging the permanent magnets symmetricallywith respect to the rotation direction, but irregularly with respect tothe depth direction, for each pole of the rotor of the permanent magnetrotating electric machine. This embodiment also makes it possible toprovide an electric vehicle that can run efficiently with a lessvibrating, less noisy motor.

Next, with reference to FIG. 14 and FIG. 15, the configuration of apermanent magnet rotating electric machine in a fifth embodiment of thepresent invention will be described. The general configuration of thepermanent magnet rotating electric machine in this embodiment is thesame as that shown in FIG. 1 and FIG. 2.

FIG. 14 is a diagram showing the structure of the stator and the rotorof the permanent magnet rotating electric machine in the fifthembodiment of the present invention and the result of magnetic fieldanalysis when magnets are inserted into the between-pole insertingholes. FIG. 15 is a diagram showing the result of magnetic fieldanalysis when a magnet is inserted into the pole-center inserting holeof the permanent magnet rotating electric machine in the fifthembodiment of the present invention. In the figures, one pole of athree-phase, 8-pole/48-slot permanent magnet rotating electric machineis shown. The reference numerals in the figures, which are the same asthose in FIG. 3, denote the same structural elements.

As shown in FIG. 14, permanent-magnet-inserting holes 34Ax, 34Bx, and34Cx are each in the shape of a convex arc toward the outer periphery ofthe rotor. They have a columnar structure with an arc-shaped crosssection. Therefore, the permanent magnets 36Ax and 36Cx, which areinserted into the permanent-magnet inserting holes 34Ax and 34Cx, alsohave a columnar structure with an arc-shaped cross section.

The rotating electric machine in this embodiment has a better effectwhen reluctance torque is large. For this reason, a plurality of slits39 are provided on the outer periphery side of the permanent magnet 36of the rotor.

FIG. 14 also shows the result of magnetic field analysis when magnetsare inserted into the between-pole inserting holes. The broken lineindicates a magnetic field.

FIG. 15 shows the result of magnetic field analysis when a magnet isinserted into the central inserting hole, that is, when the permanentmagnet 36Bx is inserted into the central magnet inserting hole 34Bx withno permanent magnet in the between-pole inserting holes 34Ax and 34Cx.The broken line indicates a magnetic field.

The torque pulsation of the permanent magnet rotating electric machinein this embodiment is as shown in FIGS. 6 and 7. The torque pulsation ofthe whole rotating electric machine may be also reduced as shown by thewaveform of the torque pulsation that is a combination of the torquepulsation shown in FIG. 6 and the torque pulsation shown in FIG. 7.

As described above, this embodiment reduces the torque pulsation byarranging the permanent magnets symmetrically with respect to therotation direction, but irregularly with respect to the depth direction,for each pole of the rotor of the permanent magnet rotating electricmachine. This embodiment also makes it possible to provide an electricvehicle that can run efficiently with a less vibrating, less noisymotor.

In the above embodiments, the number of permanent magnets (number ofpoles) need not always be eight. Nor need the number of slots in thestator always be 48. In addition, the permanent magnet need not be aNeodymium magnet. It is needless to say that the magnet has an error inangle within the allowable manufacturing range (approximately, error±1). The present invention is applied not only to an internal rotor typebut also to an external rotor type.

The permanent magnet rotating electric machine according to the presentinvention uses no skewing under a predetermined current and voltagecondition to prevent torque from decreasing and to decrease pulsationtorque to provide a less vibrating, less noisy motor.

It should be further understood by those skilled in the art thatalthough the foregoing description has been made on embodiments of theinvention, the invention is not limited thereto and various changes andmodifications may be made without departing from the spirit of theinvention and the scope of the appended claims.

1. A permanent magnet rotating electric machine comprising a stator onwhich multi-phase stator windings are provided and a rotor which isbuilt by embedding a plurality of permanent magnets internally into arotor core and which is rotatably arranged with a predetermined gap tosaid stator, a core shape of the rotor being uniform in a depth(longitudinal) direction, wherein a plurality of permanent magnets arearranged for each pole of said rotor and wherein said plurality ofpermanent magnets are symmetrical with respect to a rotation directionbut irregularly with respect to the depth direction.
 2. The permanentmagnet rotating electric machine according to claim 1, wherein, for eachpole, there are three or more permanent-magnet-inserting holes throughwhich the permanent magnets are inserted into said rotor.
 3. Thepermanent magnet rotating electric machine according to claim 1, whereina ratio of a length of one permanent magnet arrangement to a length ofanother permanent magnet arrangement in the depth direction of saidrotor is 1:1.
 4. The permanent magnet rotating electric machineaccording to claim 1, wherein θ satisfies a relationθ=(n+0.5)×τs+φ (n is an integer) wherein, for each pole of said rotor, θis an angle between between-pole permanent-magnet-inserting holes withits vertex at a center of a shaft, φ is an angle of a pole-centerpermanent-magnet-inserting hole with its vertex at the center of theshaft, and τs is a slot pitch.
 5. The permanent magnet rotating electricmachine according to claim 1, wherein, for each pole of said rotor, amagnetic flux generated from between-pole magnets equals a magnetic fluxgenerated from a pole-center permanent magnet.